IGCSE/GCSE/O & A Level/IB/University Student Forum
Qualification => Subject Doubts => IGCSE/ GCSE => Sciences => Topic started by: @d!_†oX!© on October 26, 2009, 04:51:09 am
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If we are given this test in the qualitative analysis for salts :
" Place the funnel in a test-tube.
Pour about 3 cm3 of dilute nitric
acid onto the residue contained
in the funnel. Add about 2 cm3 of
potassium iodide to the solution
collected in the tube. "
How does it show that the salt is lead carbonate???
even the mark scheme only says : " fizz / bubbles / effervescence "
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can u plz tyoe in the year of the Qp..and all other details..
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its from May/June 2007 [ http://www.freeexampapers.us/IGCSE/Chemistry/CIE/2007%20Jun/0620_s07_qp_5.pdf ] page no. 4
and By the way one more thing
in the question paper the c) part is for 2 marks and d) part is also 2 marks
bt the mark scheme says c) part is 1 mark and d) part is 3 marks...
so can that happen in any question with us..as in can they change the marks at any point of time even after our papers are over....???
and is the test for lead in our syllabus???i have only seen it in this particular paper...its not even there in th data sheet provided to us "Notes for qualitative analysis"
plss urgent help required guys!!!!!!!
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If we are given this test in the qualitative analysis for salts :
" Place the funnel in a test-tube.
Pour about 3 cm3 of dilute nitric
acid onto the residue contained
in the funnel. Add about 2 cm3 of
potassium iodide to the solution
collected in the tube. "
How does it show that the salt is lead carbonate???
even the mark scheme only says : " fizz / bubbles / effervescence "
idoide salt = yellow ppt.
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why iodide????
there is no yellow ppt...
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why iodide????
there is no yellow ppt...
lead iodide...(yellow)
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It has to be carbonate bcoz of the fizz produced on de addition of an acid.
But where da hell did lead come frm!!!!!!!
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adi see...u didn't get my question i think
according to the markscheme there is effervescence
and u r getting a yellow ppt cuzz of the potassium iodide dt u hv added nd not in d salt
and about the anions....i know dt it is carbonate [effervescence ]
but how do we find the cation???
there is no test for lead in the notes given to us by CIE
and acc. to d ms...the salt is lead carbonate..bt i dont understand how????
that's exactly my question fakex
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Okay here's da test for lead>>>>
a)Add dilute sodium hydroxide solution to a solution of the substance. White precipitate, that does dissolve as more sodium hydroxide is added.
b)Add dilute ammonia solution to a solution of the substance. White precipitate that does not dissolve as more ammonia is added.
Whereas NaOH and NH3 solution hav nt even been used in the question!
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even i know the test now....i saw it in the A levels section sm1 had posted it
bt again nothing of this sort has been done!!!!!
what to do??? :o
fakex do u remember this is the same question that cam for our preboards...
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Yes i do remember dat test. I just scored 29.5 on 40.
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adi see...u didn't get my question i think
according to the markscheme there is effervescence
and u r getting a yellow ppt cuzz of the potassium iodide dt u hv added nd not in d salt
and about the anions....i know dt it is carbonate [effervescence ]
but how do we find the cation???
there is no test for lead in the notes given to us by CIE
and acc. to d ms...the salt is lead carbonate..bt i dont understand how????
that's exactly my question fakex
ok..1st...potassium iodide is not YELLOW!!..it is WHITE in color..
u do no get the yellow ppt because of the potassium iodide..
2nd. i aint appearing for this exam..i am writing chem/6..but still..i think ewn u heat C...a white ppt and ____carbonate is left...
wen u leave the tube to cool..it appears black/grey (possibly)...and lead carbonate is also grey...but i'm still not 100% sure.
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ok..1st...potassium iodide is not YELLOW!!..it is WHITE in color..
u do no get the yellow ppt because of the potassium iodide..
2nd. i aint appearing for this exam..i am writing chem/6..but still..i think ewn u heat C...a white ppt and ____carbonate is left...
wen u leave the tube to cool..it appears black/grey (possibly)...and lead carbonate is also grey...but i'm still not 100% sure.
@ adi
1st...i know potassium iodide is WHITE....wat i said is that wen u add it to th solution...the IODIDE ions in d sol. give the YELLOW ppt...
2nd....i knw ur not appearing for p5....nd i think u might be right at this
but is there anyone who is damn sure of any answer????
@fakex...oh yeah...al of us did badly in it man!!!
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@ adi
1st...i know potassium iodide is WHITE....wat i said is that wen u add it to th solution...the IODIDE ions in d sol. give the YELLOW ppt...
2nd....i knw ur not appearing for p5....nd i think u might be right at this
but is there anyone who is damn sure of any answer????
@fakex...oh yeah...al of us did badly in it man!!!
okk..cool..maybe some1 can correctly answer it..
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okk..cool..maybe some1 can correctly answer it..
thanks for trying though!!! :) :)
plsss some1!!!!come to our rescue!!!!!! :P
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I found it somewhere :
Pb2+ (lead): Original Solution + dil HCl = white ppt, addition of water, boil :
Potassium iodide test: Solution + KI = yellow ppt
Thus , we got a yellow ppt indicating lead .
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I found it somewhere :
Pb2+ (lead): Original Solution + dil HCl = white ppt, addition of water, boil :
Potassium iodide test: Solution + KI = yellow ppt
Thus , we got a yellow ppt indicating lead .
yellow ppt...is already understood..y is lead there?
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Above was the test for lead .....
c we acidified it with nitric acid ... then d residue was taken .. water added to make a solution
Then the KI test was performed ...
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If we are given this test in the qualitative analysis for salts :
" Place the funnel in a test-tube.
Pour about 3 cm3 of dilute nitric
acid onto the residue contained
in the funnel. Add about 2 cm3 of
potassium iodide to the solution
collected in the tube. "
How does it show that the salt is lead carbonate???
even the mark scheme only says : " fizz / bubbles / effervescence "
The fact that the anion is Carbonate is established by the fact that there is effervescence on the addition of a dilute acid. You get that here:
(c) Using a spatula, place a little of C in a test-tube. Add about 2 cm3 of dilute nitric acid and test the gas.
and (d) Place the funnel in a test-tube. Pour about 3 cm3 of dilute nitric acid onto the residue contained in the funnel. Add about 2 cm3 of potassium iodide to the solution collected in the tube.
In both these cases there is effervescence when you added a dilute acid and when tested in (c) the gas was Carbon dioxide so it is definitely a carbonate. There is a yellow ppt formed in (d) possibly because of double displacement. Hence, the insoluble salt must be yellow. We know that Lead Iodide is yellow and insoluble. This fact is used to est for Iodide usually. But in this case it is a test for Lead.
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so the whole thing as a whole is the test for lead????
as in a yellow ppt finally shows lead????
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so the whole thing as a whole is the test for lead????
as in a yellow ppt finally shows lead????
Yeah Usually it is used to test for Iodide, but in this case this was ingeniously used to test for Lead.
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OK!!!!!!!!!!!!
so d yellow colour actually shows d presence of lead!!!!!!!
ohh
dts cool...didn't know dat!!!
so this provees that the salt is lead carbonate!!!!
By the way eightAs have u seen a test for lead anywhere else except here???it isn't there in the qualitative analysis notes as well!!
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OK!!!!!!!!!!!!
so d yellow colour actually shows d presence of lead!!!!!!!
ohh
dts cool...didn't know dat!!!
so this provees that the salt is lead carbonate!!!!
By the way eightAs have u seen a test for lead anywhere else except here???it isn't there in the qualitative analysis notes as well!!
No it isn't there. During the pre-boards, when we had to do this thingee. I was thinking of the significance of (d). Then I picked up the notes page, looked at all the cations first, no luck. When went to the anion section, I saw the test for Iodide. The yellow ppt thing clicked and I realized it was lead. Tough, I didnt do well in it either cos the chemicals in our school were *******. I couldnt even see limewter going milky, there was just a faint precipitate.
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yupp mann even i read many books ab tests
i did not find in them..
they had only aluminum, copper, ammonia, calcium, iron2, iron3 and zinc i guess
but i feel eightAs' logic is correct
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yaa it is correct!! ;D
thanks alot everyone!! :) :)
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By the way this was p6 question riet???
i feel i had seen the same kind somewhere??
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naaa
it's paper 5
read on the first page of d thread
may/june 2007
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ohh
so yoou appearing for practicles??
or p6 only??
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m doing paper 5 dude
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great mann
do ur best for tmr!!
p5 is practicles... rite???
if not then wat is it??
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thanks dude... :D
ya its prax
u doing p6???
BEST OF LUCK MAN!!!!!!!! :)
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thanx
and yes aadi(|AM|) and i are doing p6
iacc.to my knowledge
i donno abt others